The present invention relates to an optical scanner which reflects light from a light source and scans the reflected light.
&lt;First Prior Art&gt;
As a conventional optical scanner, Jpn. Pat. Appln. KOKAI Publication No. 63-82165 discloses an optical scanner having an arrangement like the one shown in FIGS. 45A and 45B, i.e., a deflector 300.
As shown in FIG. 45B, the deflector 300 includes a large york 328, a coil 329 wound around the york 328, and an optical deflecting element 310 placed in the space inside the york 328.
As shown in FIG. 45A, the optical deflecting element 310 includes a mirror 312, a driving coil 311, and ligaments 313 and 314. These components are integrally formed and supported by a support frame 315.
In the deflector 300, the ligaments 313 and 314 are twisted by the force exerted on the driving coil 311 owing to the interaction between a current flowing in the driving coil 311 and a magnetic field generated by the york 328 and the coil 329. As a result, the mirror 312 is vibrated at a predetermined frequency.
Light is irradiated on the mirror 312, and the reflected light is scanned one-dimensionally.
&lt;Second Prior Art&gt;
As another conventional optical scanner, Jpn. Pat. Appln. KOKAI Publication No. 6-46207 discloses an optical scanner designed to vibrate its reflecting surface by using a piezoelectric element.
As shown in FIG. 46, in this optical scanner, a cantilever constituted by a carrier material 2 and an electrode 3 is supported on a silicon substrate 1.
This cantilever constitutes a unimorph piezoelectric actuator 6. The unimorph piezoelectric actuator 6 is manufactured by sequentially forming the carrier material 2 and the electrode 3 on the upper surface of the silicon substrate 1, and forming a space 7 by etching.
A strain gage 9 is placed on the cantilever. Another strain gage 10 is placed at the fixed end of the cantilever.
The strain gage 9 is used to measure the deformation amount of the unimorph piezoelectric actuator 6. The strain gage 10 is used to obtain a reference signal for the measuring operation.
According to this optical scanner, the deformation-free distal end portion of the cantilever functions as a reflecting surface, on which light is irradiated.
The cantilever is vibrated by the unimorph piezoelectric actuator 6. As a result, light reflected by the distal end portion of the cantilever is scanned one-dimensionally.
The optical scanner as the first prior art disclosed in Jpn. Pat. Appln. KOKAI Publication No. 63-82165 requires the large york 328 and the coil 329 to obtain a sufficient driving force. The overall structure of this device is large.
Recently, demands have arisen for compact optical scanners. However, as the overall size of a scanner is reduced to meet such demands, the driving force is reduced, and hence the deflection angle of a scan beam becomes insufficient. In addition, this scanner requires a cumbersome mechanical assembly process.
The optical scanner as the second prior art disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-46207 is smaller in size than the above optical scanner. However, the deflection angle of a scan beam is not large enough to meet the future demands.
In addition, as the electric elements of this optical scanner, e.g., the electrode 3 and the electrodes of the strain gages 9 and 10 are exposed, no countermeasures are taken against aging. That is, a problem is posed in terms of maintenance of stable performance.
&lt;Third Prior Art&gt;
Still another known compact optical scanner includes a vibration input portion formed by bonding a scan portion for reflecting light, an elongated elastic deformation portion, and a piezoelectric actuator. The reflecting portion is vibrated two-dimensionally by the piezoelectric actuator to scan light.
Such an optical scanner is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 5-100175.
FIGS. 47A and 47B show the structure of a silicon substrate 1 disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-100175.
This optical scanner 1 comprises a thin plate 6 and a piezoelectric actuator 21.
On the plate 6, a vibration input portion 5, an elastic deformation portion 2, a scan portion 3, and a weight portion 3W are integrally formed.
The piezoelectric actuator 21 is formed by bonding a strain conversion element 23 to a multilayered piezoelectric element 22.
The scan portion 3 has a mirror surface 4 for reflecting a light beam.
In the optical scanner 1 having the above structure, when a voltage is applied to the piezoelectric actuator 21 bonded to the vibration input portion 5 to vibrate the vibration input portion 5, the elastic deformation portion 2 resonates, and the scan portion 3 pivots about an axial center P in FIG. 47A within the range of an angle .theta..sub.T. At the same time, the scan portion 3 pivots about an axial center Q in FIG. 47B within the range of an angle .theta..sub.B.
In this case, the piezoelectric actuator 21 vibrates the vibration input portion 5 in a vibration mode in which vibrations having a resonant frequency of a torsional deformation mode are superimposed on vibrations having a resonant frequency of a bending deformation mode. As a result, the torsional deformation mode and the bending deformation mode are amplified by the elastic deformation portion 2, and the torsional vibrations and the bending vibrations are synthesized at the scan portion 3.
In the optical scanner 1 having the above structure, two-dimensional optical scanning is realized by controlling the voltage applied to the piezoelectric actuator 21 using a driving circuit (not shown).
&lt;Fourth Prior Art&gt;
Still another known compact optical scanner uses a silicon semiconductor substrate and a helical torsion spring. This optical scanner uses an optical deflecting element for scanning light by swinging a reflector using an electromagnetic force.
Such an optical scanner is disclosed, for example, in "TECHNICAL DIGEST OF THE SENSOR SYMPOSIUM", 1995, pp. 17-20.
FIGS. 48A and 48B show the structure of the optical scanner disclosed in this reference.
This optical scanner has a reflector 34 and helical torsion springs 33, formed on a silicon semiconductor substrate 31, together with a fixing frame 50 for supporting them. These components are integrated into an optical deflecting element.
Flat coils 35 are arranged around the peripheral portion of the reflector 34. The flat coils 35 are electrically connected to electrodes 36 on the fixing frame 50 through the helical torsion springs 33.
In addition, circular permanent magnets 38 are located through a spacer insulating substrate 40 such that the direction of magnetization of each permanent magnet 38 is parallel to the reflector 34 and makes an angle of about 45.degree. with the axial direction of the helical torsion spring 33.
When an AC current is applied to the flat coil 35, a Lorentz force is generated therein owing to the interaction between the current and the magnetic field generated by the permanent magnet 38.
This Lorentz force causes the reflector 34 to swing in the twisting direction of the helical torsion spring 33.
When a current having the same frequency as the resonant frequency defined by the elastic properties of the helical torsion spring 33 and the mass and center of gravity of the reflector 34 is applied to the flat coil 35, the maximum amplitude at the current value can be obtained.
In this case, the reflector 34 is vacuum-sealed to reduce the damping coefficient.
Referring to FIGS. 48A and 48B, reference numeral 39 denotes a gas absorbent; 41, a front cover insulating substrate; 42, a lower surface insulating substrate and 32, a movable plate.
In the third and fourth prior-art techniques, there is no description concerning the durability of electric elements such as wiring layers for the optical scanner which vibrates at large deflection angles. Moreover, in the third prior art, there is no description concerning the protection of the electric elements against the atmosphere.
&lt;Fifth Prior Art&gt;
As a conventional optical scanner, there is also known a light deflecting element disclosed, for example, Jpn. Pat. Appln. KOKOKU Publication No. 60-57052. In this light deflecting element, as shown in FIG. 73, a spring portion 1002 and a movable portion 1003 supported by the spring portion 1002 are formed of a single insulating substrate 1001. The movable portion 1003 is provided with a reflection mirror 1004 and a coil pattern 1005. The spring portion 1002, movable portion 1003, reflection mirror 1004 and coil pattern 1005 are formed by photolithography and etching technique. According to this light deflecting element, the spring portion 1002 is torsion-vibrated and thereby reflected light can be scanned in a predetermined direction.
In this conventional optical scanner, wiring for supplying current to the coil pattern 1005 is formed on a surface of the spring portion 1002 or an elastic member. The reason is that in the conventional optical scanner, like the light deflecting element described in Jpn. Pat. Appln. KOKOKU Publication No. 60-57052, the spring portion 1002 is formed of single insulating substrate 1001 and thus there is no choice but to provide wiring on the surface of the spring portion 1002. In the structure wherein wiring is formed on the surface of spring portion 1002, however, there arises such a problem that when the spring portion 1002 is bent or torsion-vibrated, the wiring is adversely affected by a great stress occurring at the surface of the spring portion 1002. In general, optical scanners are so controlled that they may be reciprocally moved over and over. If a great stress acts on the wiring repeatedly, the wiring will degrade and, in a worst case, such fault as breakage of wiring will occur.